The present invention relates to centrifugal clutches. More particularly, the present invention relates to centrifugal clutches with the capability to vary torque capacity.
Clutches are used in a variety of mechanical systems to transmit torque from a motor to a driven part (e.g., drive belt or chain) of a mechanism. A clutch is a coupling used to connect and disconnect a driving and a driven part of a mechanism. A wide variety of clutches are known. A positive contact clutch transmits power from a driving shaft to a driven shaft by means of jaws or teeth. A disc clutch is able to transmit torque from an input shaft to an output shaft because of the frictional force developed between two plates or discs. A cone clutch is another type of axial friction clutch in which a cone fits in a cup. Electric clutches, hydraulic or pneumatic clutches, and overrunning clutches are also used to produce torque transmission.
A centrifugal clutch is designed to "engage" and transmit torque from an input shaft to an output shaft whenever some minimum rotational speed has been exceeded. The input shaft imparts centrifugal force to clutch shoes attached to the input shaft. The centrifugal force acts on the clutch shoes and moves the clutch shoes radially outward from the input shaft axis of rotation and into engagement with a housing connected to the output shaft. The torque capacity of a conventional centrifugal clutch is a function of the input shaft rate of rotation and the weight of the clutch shoes. It is known to attach springs between the clutch shoes to control the rate of rotation at which the clutch "engages".
It would be advantageous to provide a centrifugal clutch that can be assembled to provide a differential or equal torque capacity for opposite directions of rotation with a minimum number of parts. A centrifugal clutch with the capability of various torque capacities for opposite directions of rotation allows the output shaft to provide different torque capacities for opposite directions of rotation to an output mechanism. The cost of manufacturing is reduced and ease of assembly is increased by providing a centrifugal clutch with a minimum number of parts.
In accordance with the present invention, a centrifugal clutch includes a pair of clutch shoes and a rotor. The clutch also includes means for holding the clutch shoes and the rotor in engaged relation so that rotation of the rotor at a speed in excess of a minimum speed imparts enough centrifugal force to the clutch shoes to move the clutch shoes in a radially outwardly direction from the rotor axis of rotation to grip and rotate the holding means, thereby producing torque transmission.
Each clutch shoe is formed to include at least one drive arm-receiving pocket. The rotor includes at least one rotor arm extending into one of the drive arm-receiving pockets so that the rotor arm drives the clutch shoe to impart centrifugal force to the clutch shoe during rotation of the rotor. The drive arm-receiving pocket includes an inlet channel and a drive channel communicating with the inlet channel. An open mouth defines the inlet into the inlet channel and the rotor arm passes through the open mouth inlet and the inlet channel and includes a drive arm that extends into the drive channel.
Illustratively, one of the drive arm-receiving pockets is shaped to mate with the rotor drive arm that lies therein to either increase or decrease the torque capacity of the clutch depending upon the direction of rotation of the rotor. It is the shape of the side walls of the drive channel that contribute, in part, to achieve a change in the torque capacity of the clutch. Spaced-apart "aggressive" and "non-aggressive" cam follower walls define the drive channel. Because of their shapes, urging the rotor drive arm against an aggressive cam follower wall during rotation of the rotor in one direction will increase the torque capacity of the clutch and urging the same rotor drive arm against a non-aggressive cam follower wall during rotation of the rotor in the opposite direction will decrease the torque capacity of the clutch. The aggressive cam follower wall borders one edge of the drive channel and faces toward the open mouth and the non-aggressive cam follower wall borders another edge of the drive channel and faces away from the open mouth.
The rotor drive arm engages the aggressive cam follower wall in the clutch shoe when the rotor rotates about an axis of rotation in a first direction (e.g., clockwise) creating a force component directed radially outward from the axis of rotation to supplement the centrifugal force acting on the clutch shoes. The supplemental force created by the rotor drive arm acting on the aggressive cam follower increases the torque capacity of the clutch.
The rotor drive arm engages the non-aggressive cam follower wall in the clutch shoe when the rotor rotates in an opposite second direction (e.g., counterclockwise) creating a force component directed radially inward toward the axis of rotation to diminish the centrifugal force acting on the clutch shoes. The diminishment force created by the rotor drive arm acting on the non-aggressive cam follower wall decreases the torque capacity of the clutch.
Illustratively, the rotor includes a rotor hub and six rotor arms projecting radially outwardly from the rotor hub like spokes on a wheel. The six rotor arms include two drive arms and four retainer arms.
In preferred embodiments, the holding means provided in the clutch is a clutch drum. Each clutch shoe includes six clutch shoe pockets arranged to lie in the clutch drum so that the six clutch shoe pockets lie adjacent to the rotor. Each clutch shoe includes a top side and a bottom side. The top side is formed to include three of the six clutch shoe pockets and the bottom side is formed to include the remaining three clutch shoe pockets. On each side, a drive arm-receiving pocket is located centrally between two retainer arm-receiving pockets. One drive arm and two retainer arms extend into three of the pockets formed in one clutch shoe and one drive arm and two retaining arms extend into three of the pockets formed in the other clutch shoe.
Advantageously, each of the clutch shoes can be oriented in one of several patterns inside the clutch drum at the option of a user so that the drive arm engages either the drive arm-receiving pocket on the top side of the clutch shoe or the drive arm-receiving pocket on the bottom side of the clutch shoe. The shape of the drive arm-receiving pocket on the top side is different than the shape of the drive arm-receiving pocket on the bottom side so that the clutch has one torque capacity if the rotor drive arm extends into the "top side" drive arm-receiving pocket and a different torque capacity if the drive shoe is turned upside down in the clutch housing and the rotor arm extends into the "bottom side" drive arm-receiving pocket.
It will be understood that it is possible to change the torque capacity of a centrifugal clutch in accordance with the present invention simply by inverting the position of one or both clutch shoes inside the clutch housing when the centrifugal clutch is not in use and when the clutch shoe has differently shaped drive arm-receiving pockets on its top and bottom sides. It is also possible to change the torque capacity by changing the direction of rotation of the rotor when the rotor drive arms engage certain specially shaped drive arm-receiving pockets having aggressive cam follower walls on one side of the drive arm-receiving pocket and a non-aggressive cam follower wall on the other side of the drive arm-receiving pocket.
One option is to orient both clutch shoes bottom side up so that both rotor drive arms engage the bottom side drive arm-receiving pockets. Illustratively, the bottom side drive arm-receiving pockets have left side walls configured to provide aggressive cam followers that mate with the rotor drive arms to create supplemental forces that increase the torque capacity of the clutch when it is rotated in a first direction. Illustratively, the bottom side drive arm-receiving pockets also have right side walls configured to provide non-aggressive cam followers that mate with the rotor drive arms to create diminishment forces that decrease the torque capacity of the clutch when it is rotated in an opposite second direction. This type of pocket is sometimes called a "differential torque" drive arm-receiving pocket herein.
A second option is to orient both clutch shoes top side up so that both drive arms engage the top side drive arm-receiving pockets. Illustratively, the top side drive arm-receiving pockets have left and right side walls that are configured to produce no supplemental or diminishment forces when engaged by the rotor drive arms during operation of the centrifugal clutch. This type of pocket is sometimes called an "equal torque" drive arm-receiving pocket herein. Therefore, the torque capacity of the clutch remains the same and is neither increased nor decreased by engagement of the rotor drive arms and the walls of the top side drive arm-receiving pockets in the clutch shoes. It will be understood that in this embodiment, the torque capacity of the clutch is not varied by changing the direction of rotation of the rotor because none of the side walls of the top side drive arm-receiving pockets are configured to function as either aggressive or non-aggressive cam followers.
Of course, many other variations are possible based on the shape, configuration, and orientation of the rotor drive arms and the drive arm-receiving pockets in the clutch shoes. For example, one clutch shoe could be formed to include a drive arm-receiving pocket with an aggressive cam follower wall on one side of the drive channel and another "more aggressive" aggressive cam follower wall on the other side of the drive channel. Likewise, another clutch shoe could be formed to include a drive arm-receiving pocket with a non-aggressive cam follower wall on one side of the drive channel and another "less aggressive" non-aggressive cam follower wall on the other side of the drive channel.
Illustratively, a motor-driven power input shaft is attached to the rotor and a power output shaft is attached to the clutch drum. In operation, the motor-driven power input shaft rotates the rotor causing the rotor arms to rotate the clutch shoes. Once the rotor is turning at a fast enough speed, the rotor arms drive the clutch shoes to impart enough centrifugal force to the clutch shoes to move the shoes outwardly to grip the clutch drum containing the rotor and the clutch shoes. This gripping action causes the drum to rotate with the rotor, thereby causing the power output shaft to rotate with the power input shaft and produce torque transmission.
The torque capacity of the clutch can be varied by orienting the clutch shoes in the housing so that the rotor drive arms engage either the top side or bottom side drive arm-receiving pockets. When the rotor drive arm engages the top side drive arm-receiving pocket, the torque capacity of the clutch is solely a function of the centrifugal force acting on the clutch shoes to move the clutch shoes radially outward into engagement with the housing. When the rotor drive arm engages the bottom side drive arm-receiving pocket, the torque capacity of the clutch can be further varied by selecting one of the two available directions of rotation of the rotor. For example, rotating the rotor in the first direction of rotation (e.g., clockwise) causes the drive arm and bottom side drive arm-receiving pocket to engage and create a supplemental force that increases the torque capacity of the clutch. Alternatively, rotating the rotor in the opposite second direction of rotation (e.g., counterclockwise) causes the drive arm and bottom side drive arm-receiving pocket to engage and create a diminishment force that decreases the torque capacity of the clutch.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.